A userspace draft is a draft of an article (or part of an article) associated with a specific user account and stored in the user namespace. Userspace drafts are distinct from drafts located in WP:Draftspace. You must create a user account to create your own userspace and be logged in to use it.
Explanation:

Every registered user account on Wikipedia has its own "userspace" – for instance, User:Example/Lipsum is a page called "Lipsum" in User:Example's userspace.

Userspace is part of Wikipedia, and its use is governed by community rules, but it is not part of the encyclopedia. (The encyclopedia part of Wikipedia is called the "mainspace" – e.g. Lorem ipsum is a page in mainspace.)

For a list of all your drafts (and any other subpages you have), click on "Contributions" (at the very top right of any Wikipedia page, if you're logged in), then scroll to the bottom and click the "Subpages" link.

Note: every edit you make to a userspace draft is potentially visible online to anyone, even though it's in your own space. Whilst your edits there are 'saved' by hitting the same big, blue 'Publish changes' button you see when editing existing Wikipedia articles, don't be confused by the term 'publish' in this context. It's not the same as actually moving a draft into the main encyclopedia for everyone to find and read. Many people consider only that element as 'publishing', whereas the reality is that everything we do here is published online, whether made in a userspace, a sandbox, a draft article or in a main article.

As a courtesy, when you have a page in your userspace you no longer need, add {{db-userreq}} to the top of the page. It will be deleted shortly.

In an RfC regarding the applicability of Wikipedia:Notability to drafts within the userspace and draftspace, it was determined that community consensus amounted to "notability guidelines do not apply to userspace and draftspace drafts".